[fix](trx-frontend-http): fix APRS HDLC decoder and add debug logging

Fix three bugs in the Bell 202 AFSK demodulator preventing frame
decoding:
- Separate NRZI state from clock recovery (shared lastBit variable
  caused NRZI to always output 1)
- Buffer 1-bits in ones counter instead of pushing to frameBits
  immediately, preventing flag/stuff bits from contaminating frame
  data and corrupting byte alignment
- Detect flags via ones-count on decoded bits instead of shift
  register on raw bits

Also add framed packet log container styling, remove redundant
description text, and add debug counters logging pipeline health
to the browser console.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js

@@ -667,6 +667,15 @@ function createDemodulator(sampleRate) {
   const samplesPerBit = sampleRate / BAUD;
   const windowLen = Math.round(samplesPerBit);
 
+  // Debug counters
+  let dbgSamples = 0;
+  let dbgBits = 0;
+  let dbgFlags = 0;
+  let dbgFrameAttempts = 0;
+  let dbgCrcFails = 0;
+  let dbgFramesOk = 0;
+  let dbgLastLog = 0;
+
   // Correlation buffers
   let markI = 0, markQ = 0, spaceI = 0, spaceQ = 0;
   const ringLen = windowLen;
@@ -678,15 +687,16 @@ function createDemodulator(sampleRate) {
 
   // Clock recovery
   let sampleCount = 0;
-  let lastBit = 0;
+  let lastTone = 0;     // tone-level tracking for clock recovery
   let bitPhase = 0;
 
+  // NRZI state (separate from clock recovery)
+  let prevSampledBit = 0;
+
   // HDLC state
   let ones = 0;
   let frameBits = [];
   let inFrame = false;
-  let shiftReg = 0;
-  let bitCount = 0;
 
   const frames = [];
 
@@ -714,8 +724,8 @@ function createDemodulator(sampleRate) {
     const bit = markEnergy > spaceEnergy ? 1 : 0;
 
     // Clock recovery via zero-crossing
-    if (bit !== lastBit) {
+    if (bit !== lastTone) {
-      lastBit = bit;
+      lastTone = bit;
       // Nudge phase toward center of bit
       bitPhase = samplesPerBit / 2;
     }
@@ -723,49 +733,62 @@ function createDemodulator(sampleRate) {
     bitPhase--;
     if (bitPhase <= 0) {
       bitPhase += samplesPerBit;
+      dbgBits++;
       processBit(bit);
     }
 
+    dbgSamples++;
     sampleCount++;
   }
 
   function processBit(rawBit) {
     // NRZI decode: no transition = 1, transition = 0
-    // We track previous raw bit; same = 1, different = 0
+    const decodedBit = (rawBit === prevSampledBit) ? 1 : 0;
-    const nrziBit = (rawBit === lastBit) ? 1 : 0;
+    prevSampledBit = rawBit;
 
-    // Check for flag (0x7E = 01111110 in bit order)
+    if (decodedBit === 1) {
-    shiftReg = ((shiftReg >> 1) | (rawBit << 7)) & 0xFF;
+      // Don't push yet — buffer in ones counter until we know
-    bitCount++;
+      // these aren't part of a flag, stuff, or abort sequence
-
-    if (nrziBit === 1) {
       ones++;
-    } else {
+      return;
-      if (ones === 5) {
+    }
-        // Bit stuffing — skip this zero
+
+    // decodedBit === 0
+    if (ones >= 7) {
+      // Abort sequence — reset
+      inFrame = false;
+      frameBits = [];
       ones = 0;
       return;
     }
-      ones = 0;
+    if (ones === 6) {
-    }
+      // Flag (01111110) — frame boundary; the 6 ones are flag bits, not data
-
+      dbgFlags++;
-    if (shiftReg === 0x7E) {
-      // Flag detected
       if (inFrame && frameBits.length >= 136) {
-        // Minimum AX.25 frame: 14 addr + 1 ctrl + 1 pid + 1 info + 2 fcs = 19 bytes = 152 bits
+        dbgFrameAttempts++;
-        // But we check >= 136 bits (17 bytes) to be lenient
         const frame = bitsToBytes(frameBits);
-        if (frame) frames.push(frame);
+        if (frame) { dbgFramesOk++; frames.push(frame); }
       }
       frameBits = [];
       inFrame = true;
       ones = 0;
       return;
     }
-
+    if (ones === 5) {
+      // Bit stuffing — flush the 5 data ones, discard the stuffed zero
       if (inFrame) {
-      frameBits.push(nrziBit);
+        for (let k = 0; k < 5; k++) frameBits.push(1);
       }
+      ones = 0;
+      return;
+    }
+
+    // Normal data: flush buffered ones then push the zero
+    if (inFrame) {
+      for (let k = 0; k < ones; k++) frameBits.push(1);
+      frameBits.push(0);
+    }
+    ones = 0;
   }
 
   function bitsToBytes(bits) {
@@ -784,7 +807,12 @@ function createDemodulator(sampleRate) {
     const payload = bytes.subarray(0, byteLen - 2);
     const fcs = bytes[byteLen - 2] | (bytes[byteLen - 1] << 8);
     const computed = crc16ccitt(payload);
-    if (computed !== fcs) return null;
+    if (computed !== fcs) {
+      dbgCrcFails++;
+      console.debug("[APRS-DBG] CRC fail:", byteLen, "bytes, fcs=0x" + fcs.toString(16), "computed=0x" + computed.toString(16),
+        "first6:", Array.from(payload.subarray(0, 6)).map(b => b.toString(16).padStart(2, "0")).join(" "));
+      return null;
+    }
 
     return payload;
   }
@@ -793,6 +821,13 @@ function createDemodulator(sampleRate) {
     for (let i = 0; i < samples.length; i++) {
       processSample(samples[i]);
     }
+    // Periodic debug log every 3 seconds
+    const now = Date.now();
+    if (now - dbgLastLog >= 3000) {
+      console.log("[APRS-DBG] samples:", dbgSamples, "bits:", dbgBits, "flags:", dbgFlags,
+        "frameAttempts:", dbgFrameAttempts, "crcFails:", dbgCrcFails, "ok:", dbgFramesOk);
+      dbgLastLog = now;
+    }
     const result = frames.splice(0);
     return result;
   }
@@ -858,6 +893,7 @@ function parseAPRS(ax25) {
 }
 
 function addAprsPacket(pkt) {
+  console.log("[APRS]", `${pkt.srcCall}>${pkt.destCall}${pkt.path ? "," + pkt.path : ""}: ${pkt.info}`, pkt);
   const row = document.createElement("div");
   row.className = "aprs-packet";
   const now = new Date();
@@ -896,8 +932,12 @@ function startAprs() {
         aprsAudioCtx = new AudioContext({ sampleRate: sr });
         demodulator = createDemodulator(sr);
 
+        let aprsFrameCount = 0;
         aprsDecoder = new AudioDecoder({
           output: (frame) => {
+            if (aprsFrameCount++ === 0) {
+              console.log("[APRS-DBG] First PCM frame:", frame.numberOfFrames, "samples,", frame.numberOfChannels, "ch, format:", frame.format, "sr:", frame.sampleRate);
+            }
             const buf = new Float32Array(frame.numberOfFrames * frame.numberOfChannels);
             frame.copyTo(buf, { planeIndex: 0 });
             // Use first channel only

src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html

@@ -126,7 +126,7 @@
         <div class="plugin-item">
           <strong>APRS Decoder</strong>
           <div style="color:var(--text-muted); font-size:0.85rem; margin-top:0.2rem;">
-            Decodes APRS packets from RX audio using Bell 202 AFSK (1200 baud). Switch to the APRS tab to start.
+            Decodes APRS packets from RX audio using Bell 202 AFSK (1200 baud).
           </div>
         </div>
       </div>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/style.css

@@ -214,7 +214,7 @@ small { color: var(--text-muted); }
 .sub-tab.active { border-bottom-color: var(--accent-green); color: var(--accent-green); font-weight: 600; }
 .sub-tab:hover:not(.active) { color: var(--text); }
 .aprs-controls { display: flex; gap: 0.6rem; align-items: center; margin-bottom: 0.75rem; }
-#aprs-packets { max-height: 360px; overflow-y: auto; }
+#aprs-packets { max-height: 360px; overflow-y: auto; border: 1px solid var(--border-light); border-radius: 6px; background: var(--input-bg); font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace; }
 .aprs-packet { font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace; font-size: 0.82rem; padding: 0.35rem 0.5rem; border-bottom: 1px solid var(--border); line-height: 1.4; }
 .aprs-packet:last-child { border-bottom: none; }
 .aprs-call { color: var(--accent-green); font-weight: 600; }